Resistance wire temperature sensor and method of making same

ABSTRACT

A resistance temperature sensor adapted to be produced in a semiautomated manner and which is extremely rugged in construction. The basic lead and support element is made in long lengths and then trimmed to stock lengths and the resistance wire is then mounted and enclosed. The exact overall length of the resistance sensor can be altered to a particular customer&#39;&#39;s requirements by trimming the lead and support assembly without substantially affecting the calibration of the resistance sensor. The sensor is constructed so that it is extremely rugged and insensitive to handling, and at the same time gives high accuracy.

llnited States Patent [1 1 Carlson et a1.

[ RESISTANCE WIRE TEMPERATURE SENSOR AND METHOD OF MAKING SAMEInventors: John T. M. Carlson, Edina; Gerald P.

Lawson, Blaine, both of Minn.

Assignee: Rosemount Inc., Eden Prairie, Minn.

Filed: Oct. 4, 1971 Appl. No.: 186,001

[52] US. Cl 338/30, 29/612, 338/271,

338/302, 338/331 [51] Int. Cl H0lc 7/00 [58] Field of Search 338/28, 30,271,

[56] References Cited UNITED STATES PATENTS 2,216,375 10/1940 Minter338/30 1 Sept. 25, 1973 Primary Examiner-C. L. Albritton AttorneyRalphL. Dugger et a1.

A resistance temperature sensor adapted to be produced in asemiautomated manner and which is extremely rugged in construction. Thebasic lead and support element is made in long lengths and then trimmedto stock lengths and the resistance wire is then mounted and enclosed.The exact overall length of the resistance sensor can be altered to aparticular customers requirements by trimming the lead and supportassembly without substantially affecting the calibration of theresistance sensor. The sensor is constructed so that it is extremelyrugged and insensitive to handling, and at the same time gives highaccuracy.

ABSTRACT 8 Claims, 6 Drawing Figures Patented Sept. 25, 1973 2Sheets-Sheet 1 I 17 M K L3) 14 H1) INVENTOR.

JOHN 77M cAflsa/v y GERALD R LAwso/u.

Patented Sept. 25, 1973 :1 Sheets-Sheet :1

FIG. 1(-

PIE 5 FIG. 5

INVENTOR. JOl-M/ rm. cneasalv r2 LAWSON BY GERALD l RESISTANCE WIRETEMPERATURE SENSOR AND METHOD OF MAKING SAME BACKGROUND OF THE INVENTIONods of time, they have been adversely affected by the rough handlingwhich is frequently experienced in the industrial world. Initialinstallation and maintenance of the monitored industrial equipment afterthe sensors are installed in many instancesdamages the sensors. When thesensors are exposed to a hostile environment over an extremely longperiod of time, conventionally manufactured sensors may also be damaged.Extremely rugged temperature sensors have been developed. but these aregenerally designed for individual applications and the special designleads to, high costs. These. designs are not suited for general purposeindustrial sensors.

SUMMARY OF THEINVENTION The present invention relates to a sensingelement employing a resistance wire which lends itself to highproduction with automated equipment. The element is made up to beextremely rugged, and; the, basic assembly of the element is made indesired stocklengths. The final sensor can be adjusted in lengthto suitanindivid ual customer's requirements without substantially affectingthe calibration of thesensor.

The basicleads of the sensor also form a core support for the helicallywound resistance wire. The basic leads are trimmed in length tosuitindividual requirements. The leads are'quitelow in resistance inrelation to the sensing element itself, and therefore the adjustment'inlength of the leads does not affectthe calibration of the resistancesensing element.

The leads which support and are attacheddirectly to the resistanceelement areextremelyrugged, and avoid one troublesome area of the priorart wherein' mishandling resulted in the lead wire being torn loose fromthe resistance wire atthe point of connection. Theleads in this instanceserve as supports for the unit and are quite rugged.

The invention alsorelates'to the method of making industrial sensorswhichare accurate and yet: rugged and still low'in cost.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a part sectional viewof aninitial assembly FIG. 3 is a part sectional view;of the sensor showing astill further step in the forming;

FIG. 4 is a view of a finished sensor made according to the presentinvention with parts in section and parts broken away;

FIG. 5 is a side view of a sensor showing a connector for attaching thesensor of the present invention to industrial equipment, and

FIG. 6 is a view of a further modified attachment device used with thesensor of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring specifically to FIG.1, the temperature sensor comprises an initial lead and support assemblyillustrated generally at 10 which comprises a mandrel on which theresistance wire element is mounted. This assembly is made up of a basicinner electrical conductor lead formed of a tube or rod 12 which iscovered with an insulating sleeve 13. The insulating sleeve 13 can be ofany desired material, but preferably is of a high temperature wovenglass fiber flexible sleeving that can be easily slipped over the tubeor rod 12, as shown, in order to insulate the metallic rod 12. Anelectrical conducting tube 14 is pulled over the rod 12 and sleeve 13and tube 14 is swaged down onto the sleeve 13, and rod or tube 12 toform a solid assembly. Another sleeve of insulating material 15 (wovenglass-fiber or the like) is drawn over the tube 14, and then an outerprotective tube 16, is swaged over the prior assembly directly againstthe insulating sleeve 15. This basic lead-support assembly justdescribed is made up into long lengths, and can be made in asemiautomated or automated process. The high temperature woven glassfiber insulating sleeve will compress slightly when the swagingoperation is performed on the tubes 14 and 16.

The tube 16, when it is initially installed, is of uniform outsidediameter, which is the largest diameter thereof shown in FIG. I. Then,the support assembly is cut into pre-selected stock lengths usually onthe order of 6 to 18 inches long. Each support assembly is then machinedfor further processing. The unit is turned down so that there is asurface 17 formed on the interior support rod or tube 12, a surface 18which is the outer surface of the outer conducting tube 14, and whichforms the mandrel support'surface on which the resistance wire will bewound, preferably, and tube 16 is turned down to form an outer surfaceI9 and a shoulder. At the opposite end of the lead support assembly thesurface 17A of rod or tube 12 is exposed which is the same diameter asthe rod 12. The surface 18A of tube 14 is exposed, and a surface 19A isformed on the tube 16 and forms a small shoulder around the tube.

Now, referring to FIG. 2, there is a more detailed showing of theresistance wire support end of the assembly. In the next step" of makingthe sensor, a disc 22 of insulating material which has a central openingis slipped over the surface 17 and positioned against the shoulderformed by the tube or rod 12, the end of the insulating sleeve 13 andthe end of tube 14. A ring 24 of conducting material has a centralopening and is pressed onto the end of rod 12 around the surface 17, andis pushed against the disc 22 of insulating material. The press fitbetween the surface defining the opening in ring 24 and the surface 17holds the disc 22 in position, and makes a good electrical connectionbetween the ring 24 and the inner lead-support rod 12 while disc 22insulates the ring from tube 14. A final machining cut may be made alongsurface 18 so that the cut includes the outer surface of the ring 24 andinsulating washer 22. Then, the resistance wire or sensing element iswound into place. The resistance wire is illustrated at 20 in FIG. 2. Avery thin coating of insulating material must be placed over the surface18 prior to winding on wire 20, or else the wire 20 itself must have apreplaced insulating coating thereon so that there is electricalinsulation between the resistance wire 20 and the surface 18 (includingthe surface of ring 24). Of course, the surface 18 is on the conductingtube 14, as previously explained. Preferably, an insulated wire isutilized because high purity resistance wires are available with hightemperature insulation on the wire itself.

Alternatively disc 22 and ring 24 may be dispensed with by machiningthat end of the assembly to a tapered surface, attaching one end of theresistance wire 20 to the then tapered portion of surface 17, thencommencing the winding across the insulation 13, thence around the tubesurface 18. Sharp edges must be avoided upon the mandrel, however andthe uniform diameter provided by the embodiment illustrated is usuallypreferred.

Referring specifically to FIGS. 3 and 4, the wire 20 is started at point23 by welding or otherwise mechanically and electrically attaching theend of the wire 20 to the outer surface of the ring 24. The insulatingcoating on the wire or surface 18 is punched through so that a goodelectrical connection is made. Then the wire 20 is helically wound alongand around the surface 18 to an end point 25 where it is spot welded(electrically and mechanically attached) to surface 18. The wire 20 iswound tightly onto the surface 18 so that it will remain stationary onthe surface 18. Through the connection 23 to the ring 24 and the pressfit connection between the inner surface of ring 24 and surface 17 ofrod 12, one end of the resistance wire is electrically and physicallyconnected to the inner lead-support rod or tube 12. The other end of theresistance wire is electrically connected by junction 25 to the outersurface of the lead-support tube 14, which is also electricallyconductive. The resistance wire 20 and the entire assembly is preferablyannealed at this stage of construction. Final trimming of the resistancevalue of wire 20 can be done after annealing by spot welding theresistance wire to the tube 14 at a different position along its length,for example at position 26, to adjust the resistance of the wire to comewithin the desired limits. This spot weld 26 will effectively reduce theoverall resistance by shortening the operative length of the wire 20.

The mandrel support for the resistance wire may also be formed by thecore member 12 alone as long as the wire is insulated therefrom. In thisinstance the tube 14 would be machined away to expose either theinsulation 13 or the surface of rod 12 and the wire 20 wound on thisexposed surface with care being taken to insulate the wire from the rod12 and tube 14 except at the ends thereof. A separate insulation tube orsleeve also could be used over the rod 12 if desired.

The ends of the wire 20 are electrically attached to the rod 12 at oneend and to tube 14 at the other end as explained above. A short sectionof surface 18 could be left extending out from surface 19 for attachmentof the wire 28, and also for trimming. A conical taper also could beused from surface 18 to the surface of rod 12 or insulation 13 when theyform mandrel surfaces.

After the assembly has been annealed, and trimmed or adjusted to itsdesired value, a tube 28 which has a slight interference fit with thesurface 19 is pressed over this surface. The end of the tube 28 abuts onthe shoulder formed by surface 19 on the tube 16 and the tube 28 is thuskept in proper position, concentric with the axis of the rod 12 so thatthere is a cavity 29 formed between the inner surface of the tube 28 andthe mandrel surface which is shown as surface 18, in which theresistance wire 20 is now positioned. The inner surface of the tube 28is also spaced from the resistance wire 20 a desired amount. The cavity29 is then filled with a suitable insulating material such as a metaloxide in powder form. For example, aluminum oxide which is poured intothe cavity 29 while the sensing element is vibrated may be used. Thecavity 29 is then filled with packed insulating material and theinsulating material holds the wire 20 in place.

After filling the cavity 29 an end cap 30 is placed onto the end of thetube 28. The cap 30 includes a pilot member forming a shoulder that ispressed into the end of the tube 28. The ends of the tube 28 are thenwelded as shown to join one end of the tube 28 to the tube 16 and theother end to the cap. These welds are continuous to hermetically sealthe interior cavity 29.

The assembly now is as shown in FIG. 3. These assemblies may then beretained in stock of the manufacturer, and if a different length isneeded, all that has to be done is that the end of the assemblyextending toward the left can be trimmed off, and new surfaces 17A, 18Aand 19A formed as desired.

Assuming that the element assembly length is correct, and an order istaken for a resistance sensor, the lead wires 40 are connected in asuitable manner to the rod 12 and to the tube 14 which form the leadsfrom the resistance wire 20. The leads 40 are insulated conductors andare four in number with two leads 40 attached to each of the leadsupport members 12 and 14 thus providing a conventional four lead wireresistance temperature sensor. The wires 40 may be spot welded in placeas shown, and after the wires 40 are put into place, a tube 42 isslipped over the lead wires and over the surface 19A, and is then spotwelded as at 43. A gap or shallow groove 44 may be left, as shown inFIG. 4, in order to accommodate a snap ring or O ring for holding theentire temperature sensor assembly in some further assembly. The cavityformed by the tube 42 surrounding the leads 410 is then filled with aflexible insulating material such as the silicone rubber indicated at45. The unit then may be connected into a conventional bridge circuit.

FIG. 5 shows a very simple mounting for the sensor wherein aconventional coupling member 46 is slipped over the outer tube 16 and iswelded into place as indicated at 47. This will be to the customersspecification for the length of the sensor from its outer tip to thebase of the coupling. Then the sensing unit can be threaded into thedesired installation.

FIG. 6 also shows a means for mounting the sensor 10 of the presentinvention in a mounting location. In some instances it is desirable tospring load the sensors so that the tip of the sensing element actuallyis held with a spring force against a support or wall structure. In FIG.6, the coupling member 50 has a bore 51 that is of larger diameter thanthe outer diameter of the tube 16 of the temperature sensor assembly 10.A shoulder 54 is formed on the interior of coupling 50 and the bore oropening defined by this shoulder forms a close fit with the sensingassembly 10. A coil spring 52 is placed inside the bore 51 and abutsagainst the shoulder 54. The spring also reacts on a spring retainerring 56 welded to the tube 16. The spring urges the coupling toward asnap ring 58 which can be placed into the groove M, previously shown, tokeep the coupling from sliding off the unit in direction of the leads.The coupling is placed so that the outer end surface 57 of the sensingassembly will abut against a stop or a surface of the mounting structurefor the sensor when the coupling member 50 is inserted into place and sothat the spring 52 is compressed to urge the end 57 against the oppositewall of the structure in which the sensor is mounted. An 0 ring may beused in conjunction with shoulder 54 to provide a slidable seal, ifdesired.

The assembly can be relatively small in size, usually one-eighth toone-quarter inch in diameter, and the resistance element can be ofplatinum, nickel or other metals used for wire temperature sensingelements. A very thin coating of insulation on the element wire itselfis desirable as previously explained, in order to eliminate thenecessity-for insulating theouter surface of the tube l4'before the wireelement is mounted intop lace. The primary lead supports 12 and 14,which are connected electrically to the opposite ends of the resistancewire may be made of stainless steel and should be selected to be closelymatched in thermoelectric characteristics so that unwanted thermal EMFsare not set up in the presence of thermal gradients.

If uninsulated resistance wire is used, an insulating coating over thesurface 18 can be plasma sprayed in a coarse layer. Alternatively, onecould provide an oxide growth forming an insulating layer on the outersurface 118 of the tube 14.

The material used for filling cavity 29, while being electricalinsulation should have high thermal conductivity to insure that heat atthe outer surface of the sensor is conducted to the resistance wire.

The surface 18 on tube 14 is the preferred wire sup port mandrel surfacebecause of ease of trimming the resistance wire and because it forms alarger diameter support. if the rod or core member 12 is used as themandrel surface the ring 24 anddisc 22 can be omitted. The wire 20 hasto be insulated from the rod 112 except where the end of the wireconnects to the rod, and also the rod 12 and the wire 20 mustbeinsulated from tube 114, except the wire 20 is electrically connectedto the tube M at one end.

When the rod 12, which is one of the leads, forms the mandrel supportand tube 14 is cut away, the advantages of adjusting the overall lengthof the sensor by cutting the opposite ends of the leads withoutaffecting the calibration or resistance value is still achieved.

What is claimed is:

l. A resistance wire assembly comprising a central core member ofconductive material, a tubular conductive member positioned over saidcore member and electrically insulated from said core member, at leastone of said members forming a mandrel support, a resistance wire elementwound over said mandrel support and insulated therefrom alongsubstantially its entire length, means to electrically connect a firstend of said wire to said tubular member and a second end of said wire tosaid core member, whereby said core member and said tubular membercomprise primary electrical leads for said resistance wire element, asecond outer tubular member surrounding at least a portion of said firstmentioned tubular conductive member, an outer jacket means surroundingsaid resistance wire element in close thermal relationship thereto andcomprising a separate tubular cover fixedly attached to said secondouter tubular member and having an internal bore of larger diameter thanthe outer surfaces of said resistance wire element mounted on saidmandrel support, and heat conducting electrical insulation means fillingthe cavity between said internal bore and the outer surface of saidmandrel support.

2. A resistance wire assembly comprising a central core member ofconductive material, a tubular conductive member positioned over saidcore member and electrically insulated from said core member, a portionof said tubular member forming a resistance wire support and aresistance wire element wound over and mechanically supported on saidportion of said tubular member forming a said resistance wire support,means to insulate said wire from the tubular member along substantiallythe entire length of said resistance wire element, means to electricallyconnect a first end of said resistance wire element to said tubularmember and to electrically connect a second end of said resistance wireelement to said core member, whereby said core member and said tubularmember comprise primary electrical leads for said resistance wireelement, and outer jacket means surrounding said resistance wire elementin close thermal relationship thereto to protect said wire.

3. A resistance wire assembly comprising a central core member ofconductive material, a tubular conductive member positioned over saidcore member and extending substantially the full length of said coremember and being electrically insulated from said core member, a portionof the outer surface of said tubular member forming a mandrel support, aresistance wire element wound over said mandrel support, means toelectrically insulate said resistance wire element from said mandrelsupport along substantially the entire length of said resistance wireelement, means to electrically connect a first end of said resistancewire element to said tubular member and a second end of said resistancewire element to said core member, whereby said core member and saidtubular member comprise primary electrical leads for said resistancewire element, and outer jacket means surrounding said wire in closethermal relationship thereto to protect said resistance wire element.

4. The sensor of claim 3 wherein said means to insulate said resistancewire element comprises an insulation material coating said resistancewire element.

5. The sensor of claim 3 wherein said means to insulate said resistancewire element from said mandrel support comprises a layer of insulationmaterial on the outer surface of said mandrel support.

6. The assembly of claim 3 and a mounting member comprising a couplingadapted to be attached to a support, means mounting the coupling to saidresistance wire assembly for limited relative sliding movement, and biasmeans acting between said coupling and said resistance wire assembly toresiliently urge the resistance wire assembly in a first directionrelative to the coupling.

7. The assembly of claim 2 wherein said core member and tubularconductive member extend in direction away from said resistance wire asubstantial length in relation to the length of the mandrel support, andinsulated lead wire means electrically connected to ends of ring memberattached mechanically and electrically to said core end portion, andmeans to insulate said ring from said conducting tube, the second end ofsaid resistance wire being connected to the outer surface of said ring.

"H050 UNl'l-ED STATES PATENT @FFICE (5/69) CERTIFICATE @F QORREC'HQNPatent No. 3,7611857 Dated Sepbember 25, 1973 Inventor(5) T-Ma Carlsonet a1. 7

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

W Column 3, line 64 "28" should be--20-.' Column 4, line 22 after "cap"insert--30--. Column 6, line 17, (Claim 2 line 8) before "said"cancel--a--; Column 6, line 28, (Claim 2, line 19) before "wire"insert--resistance--; Column 6 line 45, (Claim 3, line 17) cancel "wire"and insert--resistance wire element-; Column 6, line 67, (Claim 7 line4-) cancel "mandrel" and insert--resistance wire, Column 8, line 3,(Claim 8, line 8) cancel "conducting tube" and insert--tubularconductive member--.'

Signed and sealed this 26th day of March 19714.. v

- (SEAL) Attest:

EDWARD M.FLETCHER,JR. 0.. MARSHALL DANN Commissioner of PatentsAttesting Officer 222g? UN lTED STATES PATENT CFFICE CERHFICATE OFCORREC'HCN Patent No. 3,761,857 Dated September 25, 1973 Inventor(s)JOhlfl 'I'.M. Carlson et a1,

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

r Column 3, line 64 "28" should be--20--.' Column 4, line 22 after "cap"insert--30--. Column 6, line 17, (Claim 2, line 8), before "said"cancel--a--; Column 6, line 28, (Claim 2, line 19) before "wire"insert--resistance--; Column 6, line 45, (Claim 3, line 17) cancel"wire" and insert--resistance wire element--; Column 6, line 67, (Claim7 line 4) cancel "mandrel" and insert--resistance wire--. Column 8, line3, (Claim 8, line 8) cancel "conducting tube" and insert--tubularconductive member;

Signed and sealed this 26th day of March 19m.

- (SEAL) Attest:

EDWARD M.FIETCHER,JR. 0-. MARSHALL DANN Commissioner of PatentsAttesting Officer

1. A resistance wire assembly comprising a central core member ofconductive material, a tubular conductive member positioned over saidcore member and electrically insulated from said core member, at leastone of said members forming a mandrel support, a resistance wire elementwound over said mandrel support and insulated therefrom alongsubstantially its entire length, means to electrically connect a firstend of said wire to said tubular member and a second end of said wire tosaid core member, whereby said core member and said tubular membercomprise primary electrical leads for said resistance wire element, asecond outer tubular member surrounding at least a portion of said firstmentioned tubular conductive member, an outer jacket means surroundingsaid resistance wire element in close thermal relationship thereto andcomprising a separate tubular cover fixedly attached to said secondouter tubular member and having an internal bore of larger diameter thanthe outer surfaces of said resistance wire element mounted on saidmandrel support, and heat conducting electrical insulation means fillingthe cavity between said internal bore and the outer surface of saidmandrel support.
 2. A resistance wire assembly comprising a central coremember of conductive material, a tubular conductive member positionedover said core member and electrically insulated from said core member,a portion of said tubular member forming a resistance wire support and aresistance wire element wound over and mechanically supported on saidportion of said tubular member forming a said resistance wire support,means to insulate said wire from the tubular member along substantiallythe entire length of said resistance wire element, means to electricallyconnect a first end of said resistance wire element to said tubularmember and to electrically connect a second end of said resistance wireelement to said core member, whereby said core member and said tubularmember comprise primary electrical leads for said resistance wireelement, and outer jacket means surrounding said resistance wire elementin close thermal relationship thereto to protect said wire.
 3. Aresistance wire assembly comprising a central core member of conductivematerial, a tubular conductive member positioned over said core memberand extending substantially the full length of said core member andbeing electrically insulated from said core member, a portion of thEouter surface of said tubular member forming a mandrel support, aresistance wire element wound over said mandrel support, means toelectrically insulate said resistance wire element from said mandrelsupport along substantially the entire length of said resistance wireelement, means to electrically connect a first end of said resistancewire element to said tubular member and a second end of said resistancewire element to said core member, whereby said core member and saidtubular member comprise primary electrical leads for said resistancewire element, and outer jacket means surrounding said wire in closethermal relationship thereto to protect said resistance wire element. 4.The sensor of claim 3 wherein said means to insulate said resistancewire element comprises an insulation material coating said resistancewire element.
 5. The sensor of claim 3 wherein said means to insulatesaid resistance wire element from said mandrel support comprises a layerof insulation material on the outer surface of said mandrel support. 6.The assembly of claim 3 and a mounting member comprising a couplingadapted to be attached to a support, means mounting the coupling to saidresistance wire assembly for limited relative sliding movement, and biasmeans acting between said coupling and said resistance wire assembly toresiliently urge the resistance wire assembly in a first directionrelative to the coupling.
 7. The assembly of claim 2 wherein said coremember and tubular conductive member extend in direction away from saidresistance wire a substantial length in relation to the length of themandrel support, and insulated lead wire means electrically connected toends of said core member and first mentioned tubular member oppositefrom said resistance wire.
 8. The assembly of claim 2 wherein an endportion of said core member protrudes beyond the end of said tubularconductive member at the end mounting said wire, said means toelectrically connect said second end of said wire to said corecomprising a conducting ring member attached mechanically andelectrically to said core end portion, and means to insulate said ringfrom said conducting tube, the second end of said resistance wire beingconnected to the outer surface of said ring.